I can best explain like this- 'Lamens' terms is actually 'Layman's' terms. it refers to the 'Laymen'- hired help of yesteryear that were not educated at secondary schools or other teaching academies, so often did not understand technical intricacies of higher technologically design machines or techniques. They had to be explained by the higher educated to the more simply taught employees so they could have at least a reasonable understanding of how to undertake a particular task at hand.